Ductile heat-resistant Mg-Gd-Y alloys of high strength via lamellated heterostructure

The improvement of tensile strength at elevated temperatures in light metallic alloys often compromises room temperature (RT) ductility. In this study, we focus on Mg-RE alloys to demonstrate a strategy for simultaneously achieving excellent high-temperature strength and decent RT ductility. This is accomplished by integrating a heterogeneous lamella-structure with dispersed nano-spaced stacking faults. Specifically, the small deformation but multipass hot-rolled Mg-8.5Gd-3Y-2Cu-0.5Zr (wt.%) alloys exhibit a distinctive heterogeneous lamella-structure. This structure features coarse grains interspersed with fine-grained layers and plate-shaped long-period stacking ordered (LPSO) precipitates. Such a microstructure grants the alloy a yield strength of 228 MPa at 300 °C, RT ultimate tensile strength of 538 MPa, and RT elongation of 12.2 %. The good combination of ultra-high strength and substantial ductility at RT is primarily due to the hetero-deformation induced back stress and significant activation of <c+a> dislocations. In addition, the dislocation cellular walls developed during the multipass hot-rolling process, can encourage mechanisms such as twinning and stacking faults formation. The excellent strength at high temperatures is as a result of the thermally stable LPSO particles which hinder grain-coarsening in the fine-grained layers.